The transition from vegetative growth to flowering is a crucial process during plant development that is necessary for the production of grain yield in crop plants. There are four major pathways controlling flowering time in land plants that respond to environmental or developmental cues, including photoperiodism (i.e., day length), vernalization (i.e., response to winter cold), and plant hormones (e.g., gibberellins or GA), in addition to the autonomous (environmentally independent) pathways. Except for the GA and autonomous pathways, regulation of flowering in plants generally involves two central regulators of flowering time, CONSTANS (CO) and FLOWERING LOCUS C (FLC). The FLC gene is a floral repressor that regulates flowering in response to vernalization, whereas the CO gene is a floral activator that responds to photoperiod conditions. Under inductive photoperiodic conditions, CO activity in source leaves increases expression of FLOWERING LOCUS T (FT), which translocates to the meristem to trigger expression of downstream floral activating genes, including LEAFY (LFY), APETALA1 (AP1) and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1). Other genes, such as FLOWERING LOCUS C (FLC) and TERMINAL FLOWER 1 (TFL1), act to inhibit the expression or activity of these genes.
Except for day length neutral plants, most flowering plants respond to daily photoperiodic cycles and are classified as either short day (SD) or long day (LD) plants based on the photoperiod conditions required to induce flowering. The photoperiod refers to the relative length or duration of light and dark periods within a 24-hour cycle. In general, long day plants tend to flower when the day length exceeds a photoperiod threshold (e.g., as the days are getting longer in the spring), whereas short day plants tend to flower when the day length falls below a photoperiod threshold (e.g., as the days are getting shorter after the summer solstice). In other words, SD plants flower as the days are getting shorter, while LD plants flower as the days are getting longer. Soybean is an example of a short day (SD) plant in which flowering is induced when plants are exposed to shorter daylight conditions.
Plant growers are always looking for new methods to manipulate the yield of a plant, especially to enhance the seed yield of agronomically important crops. Thus, there is a continuing need in the art for improved compositions and methods for increasing yields of various crop plants. It is presently proposed that improved crop yields may be achieved by enhancing agronomic traits related to flowering and reproductive development.